glEvalMesh2 function

Computes a two-dimensional grid of points or lines.

Syntax


void WINAPI glEvalMesh2(
   GLenum mode,
   GLint  i1,
   GLint  i2,
   GLint  j1,
   GLint  j2
);

Parameters

mode

A value that specifies whether to compute a two-dimensional mesh of points, lines, or polygons. The following symbolic constants are accepted: GL_POINT, GL_LINE, and GL_FILL.

i1

The first integer value for grid domain variable i.

i2

The last integer value for grid domain variable i.

j1

The first integer value for grid domain variable j.

j2

The last integer value for grid domain variable j.

Return value

This function does not return a value.

Error codes

The following error codes can be retrieved by the glGetError function.

NameMeaning
GL_INVALID_ENUM

Indicates that mode is not an accepted value.

GL_INVALID_OPERATION

The function was called between a call to glBegin and the corresponding call to glEnd.

Error codes

The following error codes can be retrieved by the glGetError function.

NameMeaning
GL_INVALID_ENUM

Indicates that mode is not an accepted value.

GL_INVALID_OPERATION

The function was called between a call to glBegin and the corresponding call to glEnd.

Remarks

Use glMapGrid and glEvalMesh in tandem to efficiently generate and evaluate a series of evenly spaced map domain values. The glEvalMesh function steps through the integer domain of a one- or two-dimensional grid, whose range is the domain of the evaluation maps specified by glMap1 and glMap2. The mode parameter determines whether the resulting vertices are connected as points, lines, or filled polygons.

In the two-dimensional case, glEvalMesh2, let

Δ u = (u₂ u₁)/n

Δ v = (v₂ v₁)/m,

where n, u₁, u₂, m, v₁, and v₂ are the arguments to the most recent glMapGrid2 function. Then, if mode is GL_FILL, glEvalMesh2 is equivalent to:

for (j = j1; j < j2; j += 1)

{

glBegin(GL_QUAD_STRIP);

for (i = i1; i <= i2; i += 1)

{

glEvalCoord2(iΔ u + u1 ( ) , j Δ v + v1);

glEvalCoord2(iΔ u + u1 ( ) , (j+1) Δ v + v1);

}

glEnd( ); }

If mode is GL_LINE, then a call to glEvalMesh2 is equivalent to:

for (j = j1; j <= j2; j += 1)

{

glBegin(GL_LINE_STRIP);

for (i = i1; i <= i2; i += 1)

{

glEvalCoord2(iΔ u + u1, jΔ v + v1);

}

glEnd( );

}

for (i = i1; i <= i2; i += 1)

{

glBegin(GL_LINE_STRIP);

for (j = j1; j <= j1; j += 1)

{

glEvalCoord2(iΔ u + u1, jΔ v + v1);

}

glEnd( );

}

And finally, if mode is GL_POINT, then a call to glEvalMesh2 is equivalent to:

glBegin(GL_POINTS);

for (j = j1; j <= j2; j += 1)

{

for (i = i1; i <= i2; i += 1)

{

glEvalCoord2(iΔ u + u1, jΔ v + v1);

}

}

glEnd( );

In all three cases, the only absolute numeric requirements are that if i = n, then the value computed from iΔ u + u₁ is exactly u₂, and if j = m, then the value computed from jΔ v + v₁ is exactly v₂. The following functions retrieve information relating to glEvalMesh:

glGet with argument GL_MAP1_GRID_DOMAIN

glGet with argument GL_MAP2_GRID_DOMAIN

glGet with argument GL_MAP1_GRID_SEGMENTS

glGet with argument GL_MAP2_GRID_SEGMENTS

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Gl.h

Library

Opengl32.lib

DLL

Opengl32.dll

 

 

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